Amphetamine-like chemical linked to exercise mood boosts

The anti-depressant effects of exercise could be down to a feel-good chemical also found in chocolate, say UK researchers. Their study of 20 young men suggests that phenylethylamine, which has a chemical structure very similar to amphetamine, may play a key role in the "runner's high".

Several previous studies have identified exercise as a potent anti-depressant. In April 2001, the UK government recommended that doctors consider prescribing exercise sessions as an alternative to drug treatment for patients with mild depression. But how exercise achieves its effect has not been clear, says Ellen Billet of Nottingham Trent University.

Phenylethylamine was an obvious chemical to investigate, she says. "An earlier study found that 60 to 70 per cent of people with depression had lower than normal levels. It has also been used as a drug, and has been effective at treating some patients with depression," she says. "But no one has looked at levels during exercise before."

Billet's team found that levels of a metabolite of phenylethylamine - an indicator of levels of phenylethylamine in the brain - rocketed after exercise.

Huge differences

Billet studied 20 young men who did around four hours of moderate to hard exercise every week. She asked them to stop exercise completely for 24 hours, and she measured levels of phenylacetic acid - a byproduct of phenylethylamine metabolism - in their urine over this period.

The following day, the men exercised on a treadmill, and again, she analysed their urine for the next 24 hours.

Billet found that phenylacetic acid increased by an average of 77 per cent in the 24 hours after exercise, compared with the levels measured on the previous day. However, individual differences in the increase were huge, varying from 14 per cent to 572 per cent.

Diet control

"We can't really explain this," Billet says. "But this was only a preliminary study - we didn't control tightly for diet, for example, and that could have influenced the levels."

Other researchers have suggested that endorphins - natural pain-killing chemicals - which are produced during exercise could partly account for its mood-boosting effects.

"It's possible that other chemicals are more important than phenylethylamine in terms of exercise's anti-depressant effects," Billet admits. "And it's probable that lots of different chemicals are involved - but this suggests that phenylethylamine is part of the answer."

Journal reference: British Journal of Sports Medicine (vol 35, p 342)

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